Transformers transfer electrical energy by inductive coupling between conductive windings. For example, a transformer may allow alternating voltages and/or currents of magnetically coupled inductor windings to be stepped up or down. The ratio of turns in a primary winding to those in a secondary winding determines the stepping ratio in ideal transformers. The windings may encircle a toroidal core comprising ferrite or other easily magnetized ferromagnetic material. A toroidal ferromagnetic core provides a closed magnetic loop to more efficiently contain the magnetic flux and inductively link the windings.
Manufacturers create transformers in various sizes, depending on the relevant application. If the transformer is sufficiently large, e.g., greater than three inches in size, a conventional winding machine may be used to place conductors around the toroid. If the toroid is comparable to one inch in size, conventional pull-and-hook machinery may be used to aid the hand winding process. For smaller toroids, the windings are typically all wound by hand, leading to significant manufacturing costs.
One known method to avoid hand winding a toroid is to use a split ferromagnetic core, which allows machine-made windings to be inserted. The manufacturer may then mechanically attach the ferromagnetic material pieces. This assembly method may however degrade the magnetic efficiency of the resulting device, compared with one made with a continuous unbroken toroid. Other methods embed ferromagnetic materials into a printed circuit board, which may further increase manufacturing costs compared with the use of conventional printed circuit boards. Thus, while toroidal ferrite inductors or transformers are used in many applications because of their high efficiency, difficulties related to manufacturing costs and complexities remain unsolved.
Accordingly, there is a need in the art for inexpensively winding small toroidal inductors and transformers, such as those designed for attachment to conventional printed circuit boards.